The invention relates to a cutting device and a cutting method for cutting labels, and also to a labelling apparatus which is equipped with this cutting device.
A labelling apparatus is used to provide objects, such as bottles, tins, etc., with a label. To this end, in the labelling apparatus, labels are cut by means of a cutting device from a label roll which is provided with a plurality of labels arranged one behind the other in the direction of rolling and unrolling of the endless roll, and then are applied to the objects that are to be labelled.
Cutting devices for cutting labels are known from EP 2 042 437 A1 or DE 20 2005 002 793 U1. The cutting devices comprise a rotating vacuum roller and a rotating cutting element. The cutting element has on its circumference at least one cutting tool which is preferably a cutting blade but may also be a punching tool. The labels are passed over the vacuum roller and are held on the latter by a vacuum being applied by the vacuum roller via openings which are located in the roller surface of the vacuum roller, so that the cutting element can cut the labels in a controlled manner. To this end, the vacuum roller also has counter-cutting bars, on which the label roll rests during the cutting process and with which the cutting blade can be brought into contact for the purpose of cutting through the endless roll of labels. The counter-cutting bars are formed by metal bars. The process of cutting the label or the endless roll of labels is carried out by the contact between the cutting blade and the counter-cutting bar. The metal bars are preferably incorporated in the vacuum roller in such a way that they do not protrude from the roller surface.
Furthermore, for the rotating cutting element, often at least two cutting blades are provided for cutting through the label, since in this way the rotational speed of the cutting element can be reduced while maintaining the same performance of the labelling apparatus. This is because, in the case of more than two cutting blades, the cutting element need not perform a 360° rotation from one label cut to the next, but rather in the case of two cutting blades only a rotation of 180° is required, and in the case of four cutting blades only a rotation of 90° degrees is required.
Also present on the rotating vacuum roller are preferably at least two counter-cutting bars, at which the cutting blade can make the cut through the label roll. There may also be provided for example three or four counter-cutting bars at an equal spacing from one another or at different spacings from one another. Also possible for example is an arrangement of the counter-cutting bars in which the counter-cutting bars are in each case at a spacing of 60° from one another.
In this prior art, however, there is the problem that, in the case of a label length which is unfavourable for the dimensions of the respective vacuum roller, the start of the label rests precisely on a counter-cutting bar and cannot be held by vacuum. According to the applicant's internal prior art, this leads to the situation whereby this counter-cutting bar must be removed and a suitable bar with openings must be inserted into the cutout for the counter-cutting bar in the vacuum roller, in order to generate a vacuum at the location of the bar via the openings by means of the vacuum roller. Such bars with openings must currently be produced by the user of the labelling machine or cutting device itself, but this is difficult since the openings must be made at an angle to the surface of the bar and a drill used to create the openings for example can easily break. If, in the case of a vacuum roller modified in this way, a cutting of the label roll is to take place later once again at the location at which the modified bar has been installed, then at present the modified bar must be removed again and the original counter-cutting bar must be installed.
It is therefore clear that, depending on the length of the labels, a considerable modification effort is required by the user of the labelling machine or cutting device, which proves to be disadvantageous due to time and cost aspects during the labelling of objects.
Furthermore, the described replacement of the original counter-cutting bar with a bar provided with openings is not possible on newer cutting devices since the newer cutting devices demand manufacturing tolerances which cannot be adhered to in the event of removal and reinstallation of the original counter-cutting bar by the user. On newer cutting devices, the user therefore cannot make do with the previously described modification of the labelling apparatus, so that the newer cutting device cannot be used in the case of a label length which is unfavourable for the dimensions of the respective vacuum roller.
It has also already been considered to alter the vacuum rollers so that more openings or vacuum openings are present in the roller surface of the vacuum roller. In other words, it has been considered to arrange the rows of openings or vacuum openings, which are arranged in rows perpendicular to the axis of the vacuum roller, with a closer hole spacing from one row of vacuum openings to another in the vacuum roller. However, the more openings present in the vacuum roller, the longer the time taken to clean the cutting device, which results in a longer downtime of the machine. Furthermore, in such a variant, it is impossible to solve the problem that, in the case of an unfavourable label length, the start of the label rests precisely on the counter-cutting bar or next to a vacuum opening.